1. Field
The exemplary embodiments generally relate to substrate processing apparatus and, more particularly, substrate processing apparatus with substrate centering.
2. Brief Description of Related Developments
Typical manufacturing processes for semiconductor integrated circuits may utilize robotic manipulators to cycle substrates, for example, circular silicon wafers (or any other suitable substrates), through pre-determined sequences of operations in fully automated processing equipment. Substrates may be delivered to the substrate processing equipment, also referred to as a tool, in standard transportation cassettes which house a batch of one or more substrates stored in slots. Individual substrates may then be transferred from the cassettes by a specialized pick-place robot which may be integrated into the tool. Typically, the robot holds a substrate by means of frictional force between the backside of the substrate and an end effector. In some applications, the force may be supplemented by a controlled suction-cup gripper or active gripping members disposed on the end effector.
As a result of limited, but not negligible, motion of the substrates in the cassettes during transportation, the robot may pick the substrate with undesirable eccentricity or misalignment. The difference between the actual location of the center of the substrate and the specified position on the robot end effector needs to be corrected before the substrate can be processed in the tool. Conventional methods and devices for determination and correction of eccentricity or misalignment of circular substrates may include stationary aligners, aligners built into the robot end effector, and sensors placed externally to or within a chamber through which the substrate is transported by the robot. Placement of the aligners or sensors within the chamber or on the end effector may result in chambers having larger internal volumes to, for example, accommodate the aligners and sensors or the increased size of the end effector.
It would be advantageous to provide an on-the-fly substrate centering/alignment system capable of determining eccentricity and/or misalignment of a substrate passing through a chamber while making the internal volume of the chamber as small as possible.